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Identifying Neutral/Active when wiring a caged SMPS

Electrical Engineering Asked on November 19, 2021

Just received a switch mode power supply from china and wanted to double check everything before applying power – The screw terminals coming from the cage have Live, Neutral, Ground marked with a sticker but given the fact that the Made in China label itself is misspelled ("MAED IN CHINA") I have little faith in the labels.

While ground has continuity with the external cage, I noticed that the terminal marked Neutral is connected to the internal fuse on the circuit board while to the best of my knowledge the fuse should be connected closest to the live wire – Is this just a convention or does it add safety? and can mixing Live and Neutral make a circuit less safe assuming everything is still properly enclosed in the earthed cage?

One Answer

Since you will be using an earthed mains plug, and as you have polarized mains plugs in AU, I would connect it like it says on the label. However, as most power supplies like computers supplies only have one fuse, and they are used in countries where you can connect mains plug in either orientation, so the live and neutral are not guaranteed to be in certain way, it makes little difference which way you connect it, as the input should be symmetrical otherwise.

Answered by Justme on November 19, 2021

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